Goals are (1) to increase the candidate's research skills and knowledge of the electrophysiology and pharmacology of the gastrointestinal tract and spectral analysis of physiological data, and (2) to enable the candidate to conduct studies intended to delineate the behavioral and physiological mechanisms by which environmental (social) events produce enduring alterations in gastrointestinal physiology. Specific disorders investigated are irritable bowel syndrome, infant rumination syndrome, and failure to thrive. The possible role of visceral perception and reward learning in the etiology of these disorders will be emphasized. In the proposed study of irritable bowel syndrome 100 irritable bowel patients, 50 medical controls (lactose intolerant), 50 neurotic controls, and 50 healthy controls will undergo physiological tests of myoelectric and contractile activity of the colon and psychometric tests of psychopathology, stress, illness behavior, and history of rewards for somatic complaints. The effectiveness of behavioral treatments for irritable bowel will also be studied. A second study investigates the hypothesis that there are two types of infant ruminators, one of which ruminates as a self-stimulatory behavior as a result of inadequate amounts of holding and the other of which ruminates as an operant response rewarded by parental attention. The first type, it is hypothesized, will stop regurgitating when provided with increased holding, but the second type will require punishment. The differential effectiveness of the two treatments will be compared to independent assessments of mother-infant interactions. The physiological mechanism of regurgitation will be studied by esophogeal manometry and EMG recordings. A study of failure to thrive infants investigates the effects of noncontingent holding on weight gain, social responsiveness, activity level, heart rate, and other physiological parameters using a delayed-treatment control group. A fourth study will document prospectively the contribution of mother-infant separations and amount of holding to the development of failure to thrive by monitoring the amount of holding in the hospital and after discharge in premature infants. Approximately 20% of such infants develop failure to thrive syndrome.